The Regularized WSM6 Microphysical Scheme and Its Validation in WRF 4D-Var

A cold cloud assimilation scheme was developed that fully considers the water substances, i.e., water vapor, cloud water, rain, ice, snow, and graupel, based on the single-moment WSM6 microphysical scheme and four-dimensional variational (4D-Var) data assimilation in the Weather Research and Forecasting data assimilation (WRFDA) system. The verification of the regularized WSM6 and its tangent linearity model (TLM) and adjoint mode model (ADM) was proven successful. Two groups of single observation and real sounding data assimilation experiments were set up to further verify the correctness of the assimilation scheme. The results showed that the consideration of ice, snow, and graupel in the assimilation system of the 4D-Var, as opposed to their omission in the warm rain Kessler scheme, allowed the water substances to be reasonably updated, further improving the forecast. Before it can be further applied in the assimilation of observational data, radar reflectivities, and satellite radiances, the cold cloud assimilation scheme needs additional verification, including using conventional ground and sounding observations in the 4D-Var assimilation system.